There are many useful pesticides available that have great potential and have been proven in the laboratory to be effective. Application technology, however, is often lacking for some of these compounds. Thus, many pesticides cannot be effectively dispersed into areas where they are needed in order to kill the targeted pest. In addition, many current pesticides are often applied in quantities much greater than necessary to kill the target vectors.
Bacillus thuringiensis var israelensis (BTI) is a Gram-positive bacterium which has been used successfully for several years as a biological pesticide. See U.S. Pat. No. 4,166,112. BTI is commercially available in various dry and liquid forms. (Valent BioSciences Corp., Libertyville, Ill.; Central Life Sciences, Schaumburg, Ill.). Among its commercial uses, BTI formulations are used as an insecticide against Diptera (flies and mosquitos); it is commonly used as a biological mosquito larvicide. BTI is usually distributed to larval habitats by manually applying the insecticide to a water source where the larvae reside in a briquette formulation, as an aqueous solution, or as granules or powders. Also, large scale applications to habitats are possible using planes and/or helicopters.
Despite its success in the field as a larvicide, application of BTI in an aqueous phase using commercially available mist sprayers and foggers has proven to provide less than ideal results. For example, studies involving the delivery of a water-dispersible granule formulation of BTI using a conventional mist blower (STIHL SR450) or thermal fogger (Superhawk XP thermal fogger) against larval Aedes aegypti and Culex quinquefasciatus demonstrated effective ranges that were very short, i.e., <50 feet. See, e.g., Dunford et al. (2014) Journal of the American Mosquito Control Association 30:191-198; Harwood et al. (2015) Journal of Medical Entomology, 52:663-671. The limited distribution of aqueous solutions of BTI observed in these studies is unfortunate; there exists many small, cryptic habitats in the field where mosquito larvae exist and in which it is nearly impossible to manually apply insecticide. These include, e.g., habitats such as tree holes, bromeliads, small containers, small water pockets and uncovered concrete drainage systems, trash accumulations, tires, roof gutters, vegetation such as leaf axils, leaf litter, and ground pools. In addition, various insects such as the dengue and chikungunya vector Aedes aegypti breed inside homes, in which it may be difficult to apply pesticides safely.
Thus, notwithstanding the benefits of existing means for applying insecticides such as BTI in the field, there currently remains a need for improved methods and formulations for aqueous dispersal of insecticides, including formulations comprising adulticides and/or larvicides that can be sprayed on a small scale and yet cover long distances (e.g., >100 feet). Such improved formulations and methods would facilitate the control of insects, including insects which are disease vectors, in dense forests and other habitats in which the manual application of insecticide is problematic. In particular, compositions and methods to efficiently and effectively control Diptera such as mosquitos in cryptic environments comprising the use of water-based insecticidal formulations with increased dispersal ability and lower levels of active ingredients is desired.